1. Field of the Invention
The present invention relates to fuel supply systems used mainly for vehicle engines, such as internal combustion engines.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 2007-278113A discloses a known fuel supply system. FIG. 19 is a schematic diagram showing the fuel supply system disclosed in this publication. As shown in FIG. 19, a fuel supply system 112 is equipped with a fuel pump 120 supplying fuel stored in a fuel tank to fuel injection valves 104 respectively corresponding to cylinders of an engine 106. The fuel injection valves 104 are mounted to a delivery pipe 102. The fuel pump 120 pressurizes fuel introduced from a fuel inlet port 121, and discharges it through a fuel discharge port 122. The pressure of the fuel discharged by the fuel pump 120 is adjusted by a pressure regulator 140, and the fuel is thereafter supplied to the delivery pipe 102 via pipeline 300. A pipeline 300 and a back pressure chamber 310 of the pressure regulator 140 are connected to each other by a pipeline 302. The pipeline 302 is provided with a throttle portion 303. A discharge pipe 308 is connected to the portion of the pipeline 302 between the back pressure chamber 310 and the throttle portion 303. The discharge pipe 308 is provided with a throttle portion 309. An opening and closing valve 130 is installed in a portion of the pipeline 302 on the upstream side of the throttle portion 303. When the opening and closing valve 130 is opened, the discharged fuel from the fuel pump 120 is introduced into the back pressure chamber 310 via the pipeline 302. The pipeline 300 and a pressure regulating chamber 312 of the pressure regulator 140 are connected to each other by a pipeline 304. An ECU (engine control unit) 200 controls the supply of an electric power to the fuel pump 120, and also controls the supply of an electric power to the opening and closing valve 130 in accordance with the operating conditions of the engine 106.
When the fuel pump 120 is driven, the pressure of the fuel supplied to the fuel injection valves 104 from the pipeline 300 increases. In the state in which the opening and closing valve 130 is closed, the discharged fuel from the pump 120 is not introduced into the back pressure chamber 310 of the pressure regulator 140. Since the back pressure chamber 310 is open to the atmosphere, the pressure of the back pressure chamber 310 corresponds to the atmospheric pressure. The discharged fuel from the fuel pump 120 is introduced into the pressure regulating chamber 312 of the pressure regulator 140 via the pipelines 300, 304. Thus, due to a difference between a force (back pressure) F1 applied to a diaphragm of the pressure regulator 140 from within the back pressure chamber 310 and a force (fuel pressure) F2 applied to the diaphragm from within the pressure regulating chamber 312, the diaphragm deforms. And, if F1≧F2, no fuel is discharged from the pressure regulating chamber 312. If F1<F2, the fuel is discharged from the pressure regulating chamber 312 as surplus fuel. As a result, the fuel pressure in the pressure regulating chamber 312, that is, the pressure of the fuel supplied from the fuel pump 120 to the fuel injection valves 104 (which pressure may be called “system fuel pressure”), is adjusted to a low pressure.
When the opening and closing valve 130 is opened in the state in which the fuel pump 120 is being driven, the discharged fuel from the fuel pump 120 is introduced into the back pressure chamber 310 of the pressure regulator 140 from the pipeline 302. As a result, due to the pressure of the fuel introduced into the back pressure chamber, the pressure within the back pressure chamber 310 becomes to a high pressure that is higher than the atmospheric pressure. With this, the fuel pressure within the pressure regulating chamber 312, that is, the system fuel pressure, is adjusted to a high pressure. In this way, the ECU 200 controls to open or close the opening and closing valve 130 in accordance with the operating condition of the engine 106, whereby the system fuel pressure is varied.
During stopping of the engine, when the opening and closing valve 130 is closed, the ECU 200 controls to stop the operation of the fuel pump 120, and when the opening and closing valve 130 is open, the ECU 200 controls to close the opening and closing valve 130, and then to stop the operation of the fuel pump 120. Due to this arrangement, a residual pressure is maintained in the pipeline 300 through the closing of the opening and closing valve 130, the closing of the fuel injection valves 104, and the closing of a check valve (not shown) installed within the fuel discharge port 122 of the fuel pump 120. This arrangement is incorporated for suppressing generation of vapor inside the pipeline 300 when the engine is at a high temperature, and for improving the restarting property of the engine.
In the above known art (See FIG. 19), during stopping of the engine, the fuel pump 120 is stopped in the state in which the opening and closing valve 130 is closed. Thus, it is only possible to maintain in the pipeline 300 a lowered system fuel pressure as the residual pressure. Accordingly, it is impossible to maintain in the pipeline 300 a heightened system fuel pressure as the residual pressure; in particular, the suppression of vapor generation in the fuel supply path when the engine is at a high temperature is insufficient, thus leaving room for an improvement in terms of restarting property.
Therefore, there is a need in the art for a fuel supply system that is improved in the restarting property of an engine.